What is prohibited in the joints of dryer exhaust ducts?

In the context of dryer exhaust ducts, using sheet metal screws in the joints is not allowed due to the potential for lint accumulation and fire hazards. The protruding ends of sheet metal screws can create rough surfaces that trap lint, which poses a significant fire risk since lint is highly flammable.

Instead, dryer exhaust systems should use smooth, continuous joints to minimize lint buildup and facilitate proper airflow. This helps to ensure that the exhaust is effectively vented outside and reduces the chances of fire incidents. It's also important to consider that joints should be assembled in a manner that supports easy cleaning and inspection to further mitigate risks associated with dryer duct fires.

Using alternative methods such as snap-lock fittings or other approved means creates a safer environment as these options do not have the same lint-trapping characteristics. Therefore, avoiding the installation of sheet metal screws in the joints of dryer exhaust ducts aligns with safety standards and best practices in mechanical code.